Not completely - a small subset of people interested in the main topic would have an interest in these articles, but those who find the site as a result of these articles are very unlikely to be interested in the site's main topic. I expected them to get minimal traffic.

Direct traffic to these pages from search engines has gone steadily upwards at a MUCH faster pace than traffic to the rest of the site. Now, although they represent well less than 1% of the site content, they get about 10% of traffic and generate about 5% of income (mostly adsense). Traffic enters and leaves having looked around that section, confirming the lack of interest in the rest of the site.

Basically it seems like I have stumbled into a niche I never considered, which although not as profitable as other parts of the site is an ok earner.

But what to do? I really don't want to shift the focus of this site, but a new domain on the topic in question won't have the link/age/pr advantages this section now has. Expanding it is a possibility, but would look sort of strange sat on top of the main topic.

What would you do?